Work done under this project is divided between that which deals with the developmental genetics of scute mutations in D. melanogaster, and that which is concerned with the genetics of behavior and evolutionary change. Emphasis in the scute studies centers on the seeming prevalence of simple ratios that have been noted in respect to (1) The proportions of missing bristles at various bristle sites (of which D.m. has 20), (2) the proportion of "diagonal" and "same-side" patterns of flies possessing one anterior and one posterior scutellar bristle, and (3) the proportions of flies carrying all four scutellar bristles. The behavioral and evolutionary studies involve populations being selected for resistance to NaCl and CuSO4, the mating behavior of flies from introgressive (D. pseudoobscura X D. persimilis) populations, and the behaviorally based sterility exhibited by males and females of highly inbred lines (such males and females mate readily with strangers of the opposite sex).